Conventional technology used for a file system which utilizes terminals on a network is largely divided into a network file system type and a peer-to-peer type.
FIG. 20 is a conceptual diagram for showing a network file system type file system. In the file system, a plurality of share servers and a management server are connected by a network. Each share server has physical auxiliary storage. When a client requests the file system to provide a service, the management server provides a logical file system for the client from the plurality of units of the auxiliary storage. Basically, it is assumed that each share server is always in an operating mode. As that kind of file system, the NFS (Network File System) and the AFS (Andrew File System) are known. Published Unexamined Japanese Patent Application No. 2003-248611 also discloses that kind of file system.
FIG. 21 is a conceptual diagram for showing a peer-to-peer type file system. This kind of file system has a plurality of computers, which are connected to a network, forming a virtual file system as a whole instead of having an administrative server for controlling the system. Each computer has a partial auxiliary storage. When a client requests the file system to provide a service, a file is transferred from the computers to the client in one-to-one correspondence. Basically, it is assumed that each computer is not always in an operating mode. As that kind of file system, the Gnutella and the Napster are known.
The network file system shown in FIG. 20 assumes a plurality of share servers which are always in an operating system instead of using a personal computer which is switched on and off by a user. The peer-to-peer system shown in FIG. 21 has each personal computer to unilaterally disclose a file stored therein instead of allowing the client to write in the file.
The present invention is adapted in view of the technical problem, and intends to provide a method, a file system, and a program for a server of the file system which can be applied to a file system capable of writing and reading a file with a high availability while assuming a client which may not be always operating.